In most small sludge treating plants, it is not practical to use wash water to clean the sludge conveying belts. The wash water causes hydraulic problems. In a majority of plants, either large or small, the use of water results in calcium deposition in the conveyor belt material. This material build-up in the belt necessitates cleaning with an acid wash. For plants that do not have facilities for using effluent water for cleaning, the cost of clean water becomes prohibitive and is conservation inefficient.
Other belt cleaning schemes include the use of a scraper or doctor blade, which is passed over the belt filter press or over the gravity deck. The sludge is scraped off, but cleaning the belt still requires wash water to finish the cleaning process. The scraper or doctor blade, while scraping sludge from the surface of the belt, tends to force some solid into the belt. These solids eventually end up in the wash water, adding to the inefficiency of the process by removing less than the maximum amount of solids.
The present invention reflects the discovery that placing jets of forced air adjacently below the conveyor belt during sludge treatment removes excess water from the sludge. In so dewatering the sludge, the sludge dries out, and the conveyor belt is kept clean and free of sludge contaminants. The process greatly reduces or eliminates the need for wash water; the total solids captured is greatly enhanced. In addition, it has been found that this inventive technique significantly reduces the running time of the sludge treatment process. In other words, the throughput of the sludge treatment operation is greatly increased.
While jets can be used for applying air, most often a continuous slot is provided, often cut directly into the conduit. Practicality allows for the conduit, round or square, to be slotted with a (normally) 1/4 inch opening about the width of the cloth to be cleaned. Using a square conduit, composite angle material is installed over the slot. These angle pieces are fastened to the conduit with screws or bolts in slotted openings so that they can be adjusted, thus changing the size (width) of the slot. End pieces are also installed at the point on each side of the belt that serves as a dewatering area. This prevents the air from blowing out of the sides of the system. Although a simple slot in the conduit, if pressed against the cloth, will clean the cloth as it passes over the slot, by installing the composite angle material, a sacrificial wear system is introduced. The preferred material is a composite plastic material, hard but slippery.